1. Field of the Invention
The invention relates in general to electrostatic powder coating apparatus, and more specifically, to such apparatus having a movable filter belt which cooperates with a pick-up tube to return excess powder to the powder supply.
2. Description of the Prior Art
My U.S. Pat. No. 4,257,345 discloses electrostatic powder coating apparatus having a movable filter belt extending through the interior of an enclosure. A suction device is operably connected through an exhaust plenum disposed below the portion of the filter belt within the enclosure, which causes air and excess powder within the enclosure to be drawn towards one face of the filter belt. The filter belt has a predetermined permeability which allows the passage of air therethrough to the exhaust plenum, while collecting the excess powder on the one face thereof. A cleaning device removes the excess powder from the one face of the filter belt, and, through a separator, directs the excess powder to a supply container for reapplication to the workpieces to be coated.
A second movable belt, hereinafter called the wear belt, is disposed in registry with the innermost surface of the filter belt, to prevent sliding contact between the filter belt and the exhaust plenum. This sliding contact, prior to my invention, resulted in rapid abrasion of the filter belt as the filter belt moved through the enclosure. The wear belt is formed of a coarse, monofilment, synthetic material, such as polyester, arranged in the form of a mesh or screen and having a permeability greater than or equal to the permeability of the filter belt.
While the wear belt prevents the abrasion of the filter belt and greatly extends the useful life of the filter belt, it would be desirable to prevent the wear which still occurs between the filter belt at its joint and the vacuum pick-up tube at the exit end of the enclosure. In the prior art, the ends of the filter belt are joined to form a continuous loop. The belt joint is then covered with a flap which is sewn to the outer surface of the belt, to seal any open area at the joint and to protect it from abrasion. Also, a backing material, such as a polyester mesh, is adhered to the inner side of the filter, to cover the joint area and provide strength and abrasion resistance. With this design, however, the belt is still subject to fairly rapid abrasion at the flap and where the backing material is glued to the belt, as the joint area passes under the vacuum pick-up tube.